LIP-52: claimEarnings snapshot

[kyriediculous]

What does this pull request do? Explain your changes. (required)

Specific updates (required)

• add a MerkleSnapshot contract
• add unit tests for MerkleSnapshot contract
• add claimSnapshotEarnings method to BondingManager
• add claimSnapshotEarnings unit tests
• bump ethereumjs-util library dependency from 5.1.2 to 6.0.0 and resolve incompatibilities
• MerkleTree JS class based on // https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/test/helpers/merkleTree.js

How did you test each of these updates (required) Added unit tests and integration tests

Does this pull request close any open issues? https://github.com/livepeer/LIPs/blob/master/LIPs/LIP-52.md

Checklist:

• [] README and other documentation updated
• [x] All tests using npm run test pass

[coveralls]

Pull Request Test Coverage Report for Build 432d1786-962c-4ddd-a3b3-cdee4e2458ec

• 28 of 28 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 100.0%

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Totals
Change from base Build d5bdd4ff-6f3b-48b0-b9a9-766cc685537d:	0.09%
Covered Lines:	780
Relevant Lines:	780

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💛 - Coveralls

[kyriediculous]

5d171f1 moves the logic from the modifiers into internal functions to reduce the bytecode length.

Force-pushed to rebase on top of LIP-36

[yondonfu]

Changed the base branch to streamflow since the LIP-36 branch has already been merged there.

@kyriediculous Can you resolve the conflicts and rebase to squash the fixup commits on this branch? PR looks ready to merge after that.

[yondonfu]

Just FYI looks like a few of the changes in fixup commits were dropped during the rebase. Examples:

• https://github.com/livepeer/protocol/pull/397/files#r496970771
• https://github.com/livepeer/protocol/pull/397/files#r501957068